$40 for a 7" in Satanoperca in good shape is an absolutely reasonable price. As others have said, they like groups...but will hang out with other (similar) Geos.
What other eartheaters were you planning to keep them with? tank size? They're pretty peaceful fish (and like clean, warm water).
Matt
They would be kept with my pellegrini, steindachneri and my lone abalios. Tank size would either be one of my 75s or my 150. I'm not going to get them now, since I need to do major overhaul of all of my stock(I have way too many fish and need to sell some first) but I'd like to get some in the future. They are pretty neat looking.